1. Field of the Invention
The invention relates to paired spoke bicycle wheels having an optimized rim extrusion and spoke pacing which enables lighter and stronger wheels for improved performance. By spacing tensioned spokes optimally, mechanical stress on the rim structure is minimized between rim failure from high stress concentration and rim distortion from longer distances between spokes. This enables lighter and stronger rims, the rims being optimized having a sectional shape of an irregular pentagon.
2. Description of Related Art
Several pieces of prior art describe the potential, and as yet, not optimized advantages of paired spoke bicycle wheels over a century of development. As early as 1889, the U.K. patent to Lovelace No. 3056 (Feb. 20, 1889) describes paired spokes: xe2x80x9cthe spokes the each are screwed into the hub flange is w, in a line which is a tangent to a circle somewhat smaller than the said flange, and two spokes, that is to say, one from each end of the hub, meet at the same point in the rim as shown clearly in FIG. 5 . . . xe2x80x9d. The motivation for paired spokes is explained, continuing: xe2x80x9cthus bringing the strain to bear equally upon the rim and avoiding the liability to buckle, which is attendant on the usual arrangementxe2x80x9d.
Another paired spoke reference is French patent No. 1,019,285 issued to Menet dated Jan. 20, 1953. A copy of an English translation of Menet was filed in the application which issued as U.S. Pat. No. 5,931,544. It is on this translation that the explanation herein relies, although the terminology is also recognized as consistent with the disclosure in Menet""s drawings.
Menet describes a bicycle wheel having, among other features, xe2x80x9c . . . on the rim on both sides of the median plane, perpendicular to the axis of the wheel, and arranged more or less in a straight line parallel to the axis of said wheel . . . xe2x80x9d. Menet teaches a hub, axle and paired spokes: xe2x80x9cthe spokes are distributed on the rim in groups of two, having their . . . points of attachment on the hub of the wheel almost on the same line . . . xe2x80x9d. Menet describes tensioned, paired spokes, with two ends: xe2x80x9c . . . on the threaded ends of the spokes, nuts 4 are screwed on in the usual manner . . . . On the other end the two spokes of the same group will advantageously be fastened to the hub of the wheel, at points 5 . . . xe2x80x9d.
While Lovelace described the advantage as reduced xe2x80x9cstrainxe2x80x9d, Menet""s translation uses a more dynamic description of the purpose of paired spoking: xe2x80x9cthus increasing the lateral rigidity of the wheel and freeing the rim from the abnormal torsional forces to which normal rims are subjected when used until it becomes possible to considerably ease the strain on the rims without risk of warpingxe2x80x9d and xe2x80x9cto attain as perfect a symmetry as possible of the spokes on [on] both sides of a median plane, perpendicular to the axis of the wheelxe2x80x9d.
Bicycle wheels are, of course subject to both static loads and dynamic forces, and the xe2x80x9cstrainxe2x80x9d observed by Lovelace necessarily translates to transverse changes at the rim as a tensioned spoke wheel, bearing the mass of the bicycle and rider, and acceleration and deceleration forces, contacts pavement while rolling. These dynamic forces are Menet""s xe2x80x9ctorsional forces to which . . . rims are subjected when usedxe2x80x9d. Measurements of this are suggested in the aforementioned U.S. Pat. No. 5,931,544, although the inventor herein has been unable to reproduce all of the tests described in U.S. Pat. No. 5,931,544, or its parent, U.S. Pat. No. 5,104,199. However, it is believed that the tests in these two patents were static lateral load tests, not dynamic tests. It is believed that the lack of precision resulted in rims that were unduly heavy for their strength because of their closely spaced spoked design.
Two other problems were observed in the prior art. These are not believed to have been solved by the prior art.
First, paired spokes, while producing a more even strain having advantages on a rotating wheel, have the considerable disadvantage of concentrating that strain in a small area on the rim. Menet suggests a reinforcing boss: xe2x80x9cTo reinforce the fastening of the spokes, 4 two-holed bracket 7 can be inserted between the nuts and the rimxe2x80x9d. It will be appreciated that adding material and pieces to a structure optimized for strength and weight is disadvantageous, in addition to the added expense and other inefficiency of having added components needed.
Second is the difficulty in placing paired spokes that are perfectly paired precisely opposite one another on a narrow rim. A second Lovelace patent, No. 5968 Apr. 19, 1890 anticipated one of the embodiments of Dietrich ""544: xe2x80x9cThe arrangement of spokes shown in FIGS. 4 and 5, of my aforesaid drawings cannot conveniently be applied to a narrower rim, as there is not room for the spokes to be placed opposite each other; in such cases I make two holes, one in front of the other, and near together for each pair of spokes going to opposite sides of the hub, this gives practically all the advantages of the former arrangement, while it enables the method to be applied to narrow rims.xe2x80x9d The xe2x80x9caforesaid drawingsxe2x80x9d are those in Lovelace No. 3056. The circumferential offset is shown in FIGS. 6 and 7 of the Lovelace 5968 patent and described: xe2x80x9cIn the improved arrangement for attaching spokes to the wheel rims, I make two holes in the rim one in front of the other and near together, but slightly on the skew, that is to say the holes are made in a line which is diagonal to the rim, the holes are countersunk on the inside to receive the heads of the spokes and one spoke of each pair goes to one end of the hub and the other spoke to the other end, as described in my prior specification No. 3056 of 1899.xe2x80x9d Lovelace 5968 if scaled to the proportion of modem road bicycle wheels, of about one inch, would provide circumferential spacing of about 0.3 inches.
U.S. Pat. No. 1,474,631 issued Nov. 20, 1923 to House also shows a combination of paired (13, 15) and unpaired (14) spokes on a wheel. House explains that the heavy loads on wagons or artillery carriages subject spoked wheels to forces that impose lateral or transverse loads as the wheels rotate.
Certain production paired spoke rims made by the assignee of this application, and which are outside the scope of the teachings of the aforementioned Dietrich ""544 patent have had spokes spaced about 28 mm (1.1 inches) to about 33 mm (1.3 inches). While functional, these wheels need to rely on the rim rigidity to reduce the tendency towards wheel wobble, as opposed to the invention which optimizes for reducing both stress and wobble tendency. Embodiments of Dietrich-style paired spoke wheels have typically been limited to not greater than three quarters of 1 inch (19.05 mm) while standard, non-paired spoke wheels typically have spacing of around 2 inches.
Other commercial paired spoke embodiments have been sold, but these mount spokes in a reversed manner such that the spoke head is in the side wall rim and the nipple is at the hub. These are typified in U.S. Pat. Nos. 6,196,638, 6,213,562 and 6,234,580, or with crossed wire spokes penetrating the side wall of the rim, U.S. Pat. Nos. 6,158,819 and 6,231,128. These provide a much different solution than that of the instant invention, putting more material to support the rim, at the expense of a deeper, hence heavier, structure, and using a complex hub.
The spoking of the invention solves the two problems of varying transverse loads upon rotation under axle loads, while also avoiding concentration of stress and strain on the structure of the rim by pairing spokes but spacing them sufficiently apart to decrease the loads on the rim structure to levels which permit thinner, lighter rims.
Rim sections also have need for optimized form, particularly for rear wheels used on bicycles having modem multiple speed cog sets. While symmetrically formed and symmetrically spoked rear wheels have been adequate for geared bicycles typically having five rear cogsxe2x80x94when multiplied by two front chain wheels comprising the xe2x80x9cten speedsxe2x80x9d of the post-war period through the late 1990""sxe2x80x94contemporary gear mechanisms use as many as nine or ten speeds on the rear alone. The spacing required for these mechanisms require the spacing of the cog-side hub flange a considerable distance from the bicycle""s xe2x80x9cdrop-outsxe2x80x9d upon which the axle is clampingly affixed. Traditionally xe2x80x9cdishingxe2x80x9d the rear wheel using different length spokes enabled the clearance for the cogset, while still positioning the rim and tire on the centerline of the bicycle. Positioning the on the centerline is important for proper performance, particularly braking and steering. Krampera, U.S. Pat. No. 5,228,756 discloses a not altogether satisfactory solution of drilling spoke holes off center, on an occasionally twisted rim having an otherwise generally symmetric section. The instant invention is shaped to permit the spokes to fit holes that are substantially equidistant from the rim walls as they intersect the spoke bed, thereby eliminating the need for excess material and the detrimental mass and differential strength properties thereof that result from the asymmetrically located holes of Krampera. Krampera""s alternatives use extrusions having webs of varying thickness to compensate for his asymmetry, which cause stress concentration and result in unacceptably heavy or alternatively, unacceptably strong rims. The instant rim will be referred to as an offset rim, to distinguish from the asymmetric rim of Krampera, as the instant rim optimizes weight, strength and geometry.
The invention pairs spokes but spaces them sufficiently apart to decrease the loads on the rim structure to levels which permit thinner, lighter rims. This arrangement minimizes varying transverse loads imposed on rotation under axle loads, while also minimizes concentration of stress and strain on the structure of the rim by spacing the spokes 26 mm (1.02 inches) apart. It will be understood that within the limits of the measurements provided, 26 mm mathematically converts to slightly more than 1 inch.
The new rim design of the invention increases the stiffness and durability of our wheelset while maintaining a lightweight rim. An offset spoke bed rim profile minimizes the difference in spoke angle between the drive side and nondrive side spokes while using a common brakewall width and height allows quick wheel changes without brake pad adjustment and consistent braking performance
In addition to rear rim profile, ideal spoke hole spacing, termed circumferential offset or skew in the prior art, is important for optimizing strength, minimizing weight and maximizing performance. Paired spokes additional provide ease of assembly and adjustment in that conventional wheels require adjusting three spoke tensions to adjust a hob or wobble in the rim, two drive, or right spokes and a left, or nondrive spoke.
The invention takes advantage of the discovery that at a spacing, skew or circumferential offset of 26 mm (1.02 inches) stress on the spoke bed is minimized yet distortion on the rim from a radial planexe2x80x94the center plane of the wheelxe2x80x94is also minimized, these determinations, therefore, enabling lighter and better performing rims. By comparison with prior art spacing, such as that disclosed in Dietrich ""544, of 9 mm, stress in is reduced by sixteen percent (16%).
This optimization becomes particularly problematic when dealing with a rear wheel. One condition is the desirability in manufacturing for a minimum number of different size parts. In prior art hubs, for example, one solution to the different performance of a dished drive wheel was the use of different sized flanges and potentially different sized spokes. The instant invention enables the use of similarly sized flanges and spokes for improved performance and manufacturability. Additionally, it is valuable to enable machine wheel building, but prior art hubs with spoke holes in line were not adaptable to machine wheel building because of the clearances involved. Offsetting spoke holes in the flanges circumferentially as described herein enables machine wheel building.
Because of the need to provide clearance for a cogset and the incumbent variations between the left and right side of the wheel, it has also been determined that it is possible to manufacture wheels automatically and with greater economy and efficiency by using spokes of the same length. Traditionally, hub flange spoke holes on paired spoked wheels have been coaxial, that is, with a common centerline, perpendicular to the centerline of the axle. The front wheel in the invention uses this arrangement. Traditional non-paired wheels used spoke holes evenly spaced around the flange. These arrangements all required the use of different spoke lengths to achieve the required xe2x80x9cdishxe2x80x9d of the rear wheel. However, laced, crossed spokes as shown herein can advantageously use same length spokes by imposing a slight radial offset. This, coupled with the rim offset, enables use of same-length spokes.
In addition to the circumferential offset, improvements permitted by this invention over prior paired spoke and nonpaired spoke wheels include the use of the special rear rim profile that, in a finished wheel, permits improved spoke alignment to effectively reduce xe2x80x9cdishxe2x80x9d imposed by different length and differently angled spokes, and instead achieve centered alignment of the braking surfaces and tire with combined spoke hole, flange and rim profile orientation. Common or near-common left and right spoke angles in a sectional view can reduce tension disparities between left and right side, or drive and nondrive side, spokes.